HETEROTRIMERIC G-PROTEINS, VESICLE TRAFFICKING, AND CFTR CL- CHANNELS

Previously (E. M. Schwiebert, N. Kizer, D. C. Gruenert, and B. A. Stanton. Proc. Natl. Acad. Sci. USA 89: 10623-10627, 1992), we showed that heterotrimeric G proteins regulate adenosine 3',5'-cyclic monophosphate (cAMP)-activated cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels in human airway epithelial cells. The goal of the present study was to test the hypothesis that heterotrimeric G proteins regulate vesicle trafficking and exocytosis and that these events are critical for cAMP activation of CFTR-mediated Cl- secretion. We report that cAMP stimulates exocytosis and CFTR Cl- conductance (G(Cl)) in normal but not in CF cells. Stimulation of the heterotrimeric G protein G alpha(i-2) inhibited cAMP-activated CFTR G(Cl) and exocytosis in normal cells. In contrast, inhibition of G alpha(i-2) stimulated exocytosis and allowed cAMP to stimulate CFTR G(Cl) in cells isolated from patients with cystic fibrosis (CF). Brefeldin A and nocodazol prevented cAMP-induced exocytosis and also blocked cAMP stimulation of CFTR G(Cl) in normal airway epithelial cells. Our studies suggest that the heterotrimeric G protein G alpha(i-2) regulates CFTR G(Cl) in human airway epithelial cells by modulating vesicle trafficking and the delivery of CFTR Cl- channels from an intracellular vesicular pool to the plasma membrane. Inhibition of G alpha(i-2) may be a useful therapeutic approach to target mutant Delta F508 CFTR Cl- channels from an intracellular vesicular pool to the plasma membrane and thereby correct defective Cl- secretion in CF airway epithelial cells.